The present invention relates to solid-state area imaging devices for electronic still picture cameras and more particularly to a solid-state area imaging device well suited for recording a still picture for playback on a television receiver of the interlaced scanning type.
The solid-state area imaging devices heretofore known for use in video cameras including for example IT-CCD (interline transfer-charge coupled device), FT-CCD (frame transfer-charge coupled device) and MOS (metal oxide semiconductor) devices.
As regards the IT-CCD, this device has rows of photosensitive elements arranged alternate with rows of vertical transfer registers on its photosensitive surface and thus an image light signal of an optical image is applied simultaneously to each of the photosensitive elements. However, since the transfer of output signals from the photosensitive elements must be effected separately for each of the odd and even fields thereby transferring the output signals alternately field by field so that an interlaced signal is produced, while no difficulty will be caused if a mechanical shutter is used, where a still picture is to be produced without using any mechanical shutter, any difference in the image information due to the difference in the exposure time will be caused between the fields since during the time that the output signals from the photosensitive elements for one of the fields are transferred vertically (1/60 sec.) the photosensitive elements for the other field are exposed continuously. As a result, where a moving object is shot and the video signals obtained from the resulting optical image information is recorded as a still picture, the playback of the still picture can result only in a blurred reproduced still picture.
Thus, it is necessary to playback the still picture on the basis of the video signals of only one or the other of the two fields in accordance with a pseudo-interlaced scanning system and consequently the vertical resolution of the video signals at the television receiver output is in principle reduced to about one half that obtained according to the ordinary interlaced scanning system.
In the case of the FT-CCD, the photosensitive section also serves as a transfer section so that considering a high-speed shutter, the light to the photosensitive section must be intercepted during the period of vertical transfer from the photosensitive section to the storage section and therefore a mechanical shutter must be used. However, even if a mechanical shutter is provided, due to the construction of the FT-CCD, the light can be received effectively at a place corresponding to only one or the other of the fields so that even if the video-signals of this single field are subjected to the pseudo-interlaced scanning and the still picture is reproduced on a television receiver, theoretically the vertical resolution is about one-half the interlaced output as in the case of the IT-CCD.
Then, consider a case where the number of the vertical transfer registers in the existing IT-CCD is doubled so as to increase the vertical resolution of a still picture. In this case, while 525 scanning lines required for one frame of the American TV system standards, for example, can be obtained for the light signal of the still picture, the number of the horizontal readout stages is one and thus the odd and even field signals are generated alternately line by line. Then, to apply to the television receiver, the input signals must be such that the interlacing signals or the odd field signals O.sub.1, O.sub.2, . . . O.sub.262 are applied continuously and then the even signals e.sub.1, e.sub.2, e.sub.262 are applied continuously and thus the output must be converted to the required interlacing signals by a signal processing unit. This signal processing must be such that from the odd and even field signals generated alternately line by line, that is, the signals O.sub.1, e.sub.1, O.sub.2, e.sub.2, . . . , only the odd field signals and the even field signals, respectively, are extracted. In other words, it is necessary that signals O.sub.1, BL, O.sub.2, BL, O.sub.3, BL, . . . O.sub.262 and e.sub.1, BL, e.sub.2, BL, e.sub.3, BL, . . . e.sub.262 are generated (each BL representing a blank) and then the operation of reducing the time intervals of the blanks BL in the odd and even fields is performed thereby producing the required odd field signals O.sub.1, O.sub.2, O.sub.3, . . . , O.sub.262 and even field signals e.sub.1, e.sub.2, e.sub.3, . . . e.sub.262. Thus there is the disadvantage of requiring a very complicate signal processing.
It is apparent that the FT-CCD, MOS device, CPD (charge priming device), etc., also include the single-stage horizontal readout CCD and thus they have the same disadvantage as mentioned above.